Modified multiphase bitumen composition and floor covering

ABSTRACT

A floor covering having a bitumen composition as a backing layer, such as carpet tiles, which bitumen composition comprises straight run bitumen and a mixture of high density and low density polyethylene polymers blended and dispersed in the straight run bitumen as a continuous phase in an amount of up to about 12% by weight and which bitumen composition contains a minimum of about 40% by weight of a mineral filler material, such as limestone, and the bitumen composition having improved dimensional stability, adhesion, static loading and electrical conductivity and having lower cost and processing advantages.

REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of U.S. Pat. No. application Ser. No.08/283,031, filed Jul. 29, 1994, now U.S. Pat. No. 5,470,630, which is adivisional application of U.S. patent application Ser. No. 08/191,802,filed Feb. 3, 1994, now U.S. Pat. No. 5,366,779, issued Nov. 22, 1994,which is a continuation-in-part of U.S. patent application Ser. No.07/930,608, filed Sep. 29, 1992, now abandoned, which is the nationalphase of PCT International Application No. GB91/00553, filed Apr. 9,1991, which is based on Great Britain Patent Application No. 9008166.2,filed Apr. 10, 1990.

BACKGROUND OF THE INVENTION

Oxidized and polymer-modified bitumens are frequently used as a backingmaterial in the manufacture of carpet tiles. The construction of thesetiles are fairly complex and may consist of a fibrous, e.g. tufted,primary cloth which has been impregnated with a cured latex to stabilizethe tufting, and laminated to a secondary backing cloth using theaforementioned bitumen.

In this application, severe physical demands are placed on the bitumento control stress relaxation in the primary tufting cloth, to maintainand retain critical physical dimensions over a wide range of possibleapplication conditions, to prevent excessive build up to staticelectricity which may damage electrical and computer hardware as well asphysical discomfort to building occupants; and to maintain physicaldimensions under static loading conditions such as would occur whenheavy objects are placed on carpet tiles over an extended period oftime.

The bitumen used must also possess characteristics in the molten phasewhich will allow easy preparation and processing, i.e. a suitableviscosity at application temperatures with maximum thermal stability andminimum dimensional instability when applied to the manufacturedproduct.

It has been proposed in U.K. patent application GB 2 219 802 A(Vulcanite Ltd.) to incorporate a low density polyethylene into bitumenfor roofing and carpet tile backing purposes. It has been found thatsuch blends do not fulfill all of the demands placed on a bitumen usedin the contact of a carpet tile backing. The static loading anddimensional stability of a carpet tile produced using such a bitumenwould not be commercially acceptable and would fall outside the standardrequirements laid down by the carpet tile and floor laminating industry.

Self-adhesive bitumen compositions containing polyethylene orcrystalline polypropylene have been suggested for use in carpet tileswith a self-adhesive backing in GB Patent 1 417 571 (Ruberoid Ltd.).Further, carpet tiles have been prepared employing a blend of bitumenand a minor amount of a thermoplastic styrene-butadiene-styrene blockcopolymer (SBS) as the integral backing layer styrene-butadiene-styreneblock copolymer (SBS) as the integral backing layer in U.S. Pat. No.4,201,812 (Shell Oil Company). However, the block copolymer presentsprocessing, compatibility, cost and other difficulties in its use as acarpet backing blend.

SUMMARY OF THE INVENTION

This invention relates to bitumen compositions having improveddimensional stability, adhesion, static loading and electricalconductivity characteristics, particularly, but not exclusively, suchcompositions for use in the production of carpet tiles, flooring andother laminating applications.

According to the present invention, there is provided a floor coveringhaving a bitumen composition as a backing layer and a method ofpreparing the floor covering which fulfills all of the demands describedearlier and also provides considerable cost saving advantage oversystems described earlier and already in operation.

The present invention comprises a floor covering having bitumencomposition backing layer, which bitumen composition comprises:

a) dispersed phase of straight run bitumen;

b) a continuous phase of a mixture of low density polyethylene and ahigh density polyethylene;

the bitumen composition having a softening point of about 110° C. to128° C. and a penetration value of about 10 dmm to 15 dmm.

The present invention also comprises a method of preparing a floorcovering having a bitumen composition backing layer and a fibrous facesurface and a back surface, the bitumen composition backing layer bondedto the back surface. The method comprises admixing a heated, straightrun bitumen with a mixture of a low density and high densitypolyethylene to provide a homogeneous dispersion with the straight runbitumen as the dispersed phase in a continuous phase of the polyethyleneto provide a bitumen backing composition having a softening point ofabout 115° C. to 128° C. and a penetration value of about 10 to 15 dMm.The method includes heating the bitumen backing composition, forexample, to a temperature of about 160° C. to 180° C. at a coatingapplication station, applying the heated bitumen backing composition tothe back surface of the floor covering and recovering a floor covering,such as a carpet tile, having the bitumen composition as the backinglayer.

In one embodiment, this invention relates to a bitumen-polymer fillerblend suitable for use as a flooring of a laminate backing layer. Theblend may comprise a minimum inert filler material content of about 40%w/w of the final blend. The bituminous component comprises a straightrun bitumen typically of high asphaltene and resin content with apenetration value (IP 49/83) of up to 200 dmm, and also containing amixture of low density and high density polyethylenes. Generally, thetotal polyethylene content does not exceed about 12%, such as 10% w/w,of the final blend.

The present invention provides a bitumen composition useful as a backinglayer for carpet tiles which composition is low cost and can bemanufactured from locally available materials, that is, straight runbitumen rather than blown or oxidized bitumen and either virgin orpreferably low cost scrap or recycled polyethylene as a modifier. Lowcost, branched chain polyethylene, readily available scrap material, ispreferred. The bitumen-polyethylene blends employed as a backing layerprovide carpet tiles of improved dimensional stability and betterelectrical conductivity, so that an antistatic agent may not be requiredto meet existing IBM/ICL standards for conductivity.

In addition, the bitumen-polyethylene composition provides betteradhesion due to the increased tackiness of the bitumen composition, sothat there is an improved quality of lamination between the bitumenbacking layer and the back surface of the latex-coated and cured,primary, needle-punched or tufted backing sheet. The bitumen compositionpermits a reduction in the application or coating temperature, resultingin energy savings and permitting the use of less expensive, lowermelting point secondary backing sheets on the back surface of the tile,for example, the use of non-woven polypropylene sheets in place ofhigher melting point polyester or polyester-polypropylene backingsheets. The carpet tile produced has a fibrous face surface and a backsurface integrally bonded to the bitumen composition as a backing layerand typically a secondary backing sheet secured to the back surface ofthe bitumen backing layer.

In comparison to the use of styrene-butadiene-styrene block copolymers,there are no problems relating to bitumen compatibility, the bitumen isnot temperature sensitive, does not cross link in prolonged storage athigh temperature and does not require a special bitumen composition withhazardous components.

The bitumen-polyethylene blend composition used in the invention shouldhave a softening point of about 110° C. to 128° C., e.g. 115° C. to 124°C., and a penetration of about 10 dmm to 15 dmm, e.g. 10 dmm to 12 dmm.The softening point (ring and ball test) and penetration values aremeasured in accordance with the Institute of Petroleum specifications,respectively IP 58/83 and IP 49/83. The bitumen composition is preparedby heating the bitumen to about 180° C. to 200° C., e.g. 190° C., andthe polyethylene polymers are then added, typically with the highdensity polyethylene added first and the polyethylene polymer mixed withcontinuous agitation with moderate shear for sufficient time e.g. over60 minutes, until a smooth homogeneous dispersion is obtained, that is,until the bitumen is dispersed as a dispersed phase in a continuousphase of the polyethylene. Generally, the quality of the dispersion maybe monitored wherein a sample of the blend is viewed under ultravioletillumination to affect fluorescence of the polymer so the quality of theblend can be visually assessed.

The bitumen composition is employed as a backing layer for floorlaminates, particularly carpet tiles, by heating the bitumen compositionand applying one or more coating layers to the back surface of a fibrousface floor surface covering. Generally,the bitumen composition isapplied at a temperature of 160° C. to 180° C., e.g. 165° C. to 170° C.,at the coating or application station, which is a lower than normalcoating temperature with blown bitumen, and at a viscosity of 6,000 cpup to about 125,000 cp (6 to 125 pascal seconds), e.g. 20,000 cp to40,000 cp (20 to 45 pascal seconds). Generally, SBS-modified bitumensare applied as backing layers at temperatures of 180° C. to 190° C.;however, at lower temperatures of 160° C. to 170° C. and less, theviscosity of the high density polyethylene (HDPE) and low densitypolyethylene (LDPE) modified straight run bitumen does not increase asrapidly as the viscosity of blown or oxidized bitumen, so thatapplication at lower temperatures with resulting savings in energy costand the use of less expensive secondary backing are obtained. The lowerapplication temperature permits the use of low melting point, 160° C. to170° C., 100% polypropylene, non-woven or other sheet material as asecondary backing. The bitumen may be applied in any manner, such as bythe lick roller, a lay-in technique, or a knife coater. Where a lickroller applicator is used, a lower viscosity bitumen composition isemployed, e.g. 6 to 40 pascal seconds, while a knife coater permits theuse of a higher viscosity bitumen composition, e.g. 10 to 100 pascalseconds.

The bitumen composition employs straight run bitumen generally of highasphaltene and resin content and which may have penetration of up to 200dmm or less, typically less than about 100 dmm, e.g. 30 dmm to 60 dmm,particularly 40 dmm to 60 dmm. Straight run bitumen is more readilyavailable and of lower cost and lower viscosity than blown bitumen.Generally, the bitumen consists of all straight run bitumen; however,very minor amounts, for example, up to about 10% by weight of otherbitumens, such as blown bitumen or other hydrocarbon products, can beincorporated if desired.

The straight run bitumen is blended with a mixture of high density andlow density polyethylene polymers in an amount sufficient to form adominant, continuous phase of the polyethylene polymer. Once thepolyethylene concentration has reached the phase transition level,further polyethylene polymer addition, does not increase the softeningpoint of the bitumen blend. Generally, the polyethylene is employed intotal amounts of up to about 12% by weight, e.g. between 8% to 10%. Forexample, the HDPE may range from about 0.5% to 3.0% by weight, such as1% to 2%, while the LDPE may range from about 3.0% to 9.5% by weight,such as 3% to 6% or higher, where a higher penetration value, straightrun bitumen is used, but generally less than 12% w/w. It has been foundthat the use of a moderate density polyethylene to reduce the softeningpoint of the straight run bitumen is not satisfactory due to the largeconcentrations required, and that processing and cost factors make itsuse unsatisfactory. The use of low density polyethylene alone is alsonot satisfactory to produce a commercially acceptable bitumen backingcomposition for carpet tile of defined penetration value and softeningpoint.

The properties of polyethylenes are dependent upon their molecularconfigurations, molecular weights and molecular weight distributions. Animportant factor is the selection and blending of the polyethylenesused. Commercially, polyethylenes are graded in terms of the density andthe melt flow index, with both measurements necessary to define anyparticular grade. The melt flow index (MFI) is the number of grams of apolymer that can be forced through a 0.0825-inch (2.1 mm) orifice in 10minutes at 190° C. by a pressure of 2,160 grams (ASTM D1238-70).

Typically, the high density polyethylene component should have a densitybetween about 0.935 g/cm³ and 0.970 g/cm³, and a melt flow index greaterthan about 0.2, such as 0.2 to 10, e.g. 4 to 8. The low densitycomponent of this invention should have a density of about 0.90 g/cm³and 0.93 g/cm³, and a melt flow index greater than about 0.2, such as0.5 to 5.0.

Generally, the bitumen composition includes an inert mineral fillermaterial to reduce cost and to prevent cold flow of the composition inuse, such as the use of slate dust or limestone, in amounts of greaterthan about 40% by weight, such as between about 40% to 65% by weight,and typically 50% to 55%. The bitumen composition may contain a widevariety of various modifiers and additives commonly used in carpet tilebacking layers, provided such modifiers and additives are notdetrimental to the accepted quality of the backing layer. Such modifiersand additives may include, but not be limited to: antistatic agents,such as fatty amines; and carbon black, including master batch mixturesof polyethylene and carbon black, for example, HDPE and LDPE with carbonblack used for incorporating into the bitumen blend; other fillers;pigments for color; and minor amounts of other polymers and additives.

The invention will be described for the purposes of illustration only inconnection with certain embodiments; however, it is recognized thatvarious changes, modifications, additions and improvements may be madeto the invention as illustrated by a person skilled in the art, allfalling within the spirit and scope of the invention.

DESCRIPTION OF THE EMBODIMENTS

A Hubis mixer was charged with 311 Kg of 50 penetration (IP 49/83)straight run bitumen at 190° C., and 28 Kg of LDPE (MFI 3, density 0.92g/cm³), and 10.5 Kg of HDPE (MFI 4, density 0.95 g/cm³) were added, andthe mixing cycle started. After 10 minutes, a sample of the blend wasremoved for ultraviolet examination of assess blend quality. The mixingwas then continued in 10-minute cycles until no further improvement inthe quality of the dispersion could be observed. When this point wasreached, 350 Kg of limestone filler was added to produce a final batchweight of 700 Kg.

The batch was used to manufacture sample tiles employing a lick rollerto apply the bitumen to the back surface of a flooring substrate withthe bitumen temperature at the application point of 153° C. to 162° C.The polyethylene-bitumen composition had a softening point of 121° C.(IP 58/83), a penetration of 10 dmm (IP 49/83), and a viscositytemperature profile as follows:

    ______________________________________                                        Viscosity       Temperature                                                   (pascal seconds)                                                                              (C.°)                                                  ______________________________________                                        47.0            130                                                           30.0            140                                                           20.0            150                                                           14.0            160                                                           9.5             170                                                           7.5             180                                                           6.0             190                                                           ______________________________________                                    

Dispersion Quality

It was found that the best obtainable dispersion was produced after 20to 30 minutes, using the high speed disintegrator. Carpet tiles somanufactured were compared with similar commercial carpet tiles known asCollage (a trademark of Interface Flooring Systems, Inc.) as a controltile and made in the same manner, except with blown bitumen applied at190° C.

    ______________________________________                                                      Collage      Polymer-Modified                                   Results       Control Tile Tile                                               ______________________________________                                        Full Scale Industrial Trial                                                   Aachen Test                                                                   Change in dimensions                                                                        Wa.1 N.A.    Wa.1 - .02                                         after 24 hours                                                                              Wa.2 N.A.    Wa.2 - .04                                         conditioning  Wt.1 N.A.    Wt.1 + .02                                                       Wt.2 N.A.    Wt.2 - .02                                         Change in dimensions                                                                        Wa.1 - .106  Wa.1 - .130                                        after 2 hours at 60° C.                                                              Wa.2 - .121  Wa.2 - .016                                                      Wt.1 - .029  Wt.1 - .012                                                      Wt.1 - .016  Wt.2 - .022                                        Change in dimensions                                                                        Wa.1 - .068  Wa.1 - .063                                        after 2 hours water                                                                         Wa.1 - .084  Wa.2 - .020                                        at 20° C.                                                                            Wt.1 .001    Wt.1 - .033                                                      Wt.2 .002    Wt.2 - .031                                        Change in dimensions                                                                        Wa.1 - .230  Wa.1 - .166                                        after 24 hours 60° C.                                                                Wa.2 - .244  Wa.2 - .186                                                      Wt.1 - .140  Wt.2 - .014                                                      Wt.2 - .072  Wt.2 - .056                                        Change in dimensions                                                                        Wa.1 - .266  Wa.1 - .126                                        after 48 hours                                                                              Wa.2 - .228  Wa.2 - .178                                        reconditioning at                                                                           Wt.1 - .117  Wt.1 - 0                                           20° C., 65% RH                                                                       Wt.2 - .068  Wt.2 - .034                                        ______________________________________                                        Limitations of + 0.2% to - 0.4% are generally acceptable,                     except for U.S.A. and France, + 0.1% to - 0.2%.                               Tuft Withdrawal Test                                                          Mean force required                                                                         4.26 Newtons 4.40 Newtons                                       to remove tuft                                                                Static Conductivity Test                                                      Conditions: 19.9° C., 29% Relative Humidity                            IBM           1.2 × 10*11 ohms                                                                     7.75 × 10*10 ohms                            ICL           1.2 × 10*11 ohms                                                                     2.9 × 10*11 ohms                             ______________________________________                                    

Adhesion/Delamination Test

Again, the adhesion within the polymer-modified tile proved to besuperior to that exhibited within the oxidized tile.

It has been found that satisfactory commercial carpet tiles having abitumen backing composition prepared in accordance with the inventionare prepared employing a straight run bitumen with a penetration valueof 50 dmm and using an admixture of 3.6% recycled LDPE (density0.90-0.92, MFI 0.7-1.5 grams per 10 minutes) and 1.6% w/w recycled HDPE(density 0.93-0.95, MFI 6.0-8.0 grams per 10 minutes) and with the useof 55% w/w of filler material. The bitumen backing composition isapplied to the back surface of a floor covering by a lick roller at anapplication temperature of 168° C. to 175° C. at a processing viscosityof about 25 to 30 pascal seconds at 165° C.

The low and high density polyethylene-modified straight run bitumenblend provides a unique bitumen backing for floor laminates and providesenergy savings, processing and manufacturing advantages.

What is claimed is:
 1. A multiphase modified bitumen composition, whichcomposition comprises:a) a straight run bitumen; b) a polymer mixture,the polymer mixture consisting essentially of a major amount of a lowdensity polyethylene polymer (LDPE) and a minor amount of a high densitypolyethylene polymer (HDPE); c) the straight run bitumen forming adispersed phase in a continuous phase of the polymer mixture; and d) thepolymer mixture employed in an amount of up to about 12 percent byweight of the bitumen composition.
 2. The composition of claim 1 whereinthe straight run bitumen has a penetration value of up to 200 dmm. 3.The composition of claim 1 wherein the low density polyethylene isemployed in an amount of about 3 to 9.5 percent of the bitumencomposition.
 4. The composition of claim 1 wherein the high densitypolyethylene is employed in an amount of from about 0.5 to 3 percent byweight of the bitumen composition.
 5. The composition of claim 1 whereinthe bitumen composition has a softening point of about 110° C. to 128°C.
 6. The composition of claim 1 wherein the high density polyethylenehas a melt flow index of greater than about 0.2 gr/10 min. and the lowdensity polyethylene has a melt flow index of greater than 2 gr/10 min.7. The composition of claim 1 wherein the composition includes a inertmineral filler therein.
 8. The composition of claim 1 wherein thecomposition comprises a bitumen composition layer and includes anon-woven sheet material bonded to a surface of the layer.
 9. Thecomposition of claim 1 wherein the composition is characterized byviscosity of between about 6 to 125 pascal seconds at a temperature of160° C. to 180° C.
 10. A covering which comprises a sheet materialhaving the modified multiphase bitumen composition of claim 1 as acoating layer.
 11. The covering of claim 10 wherein the coveringcomprises a carpet tile having a fibrous face surface and a back surfacewherein the composition of claim 1 is secured to the back surface as abacking layer.
 12. The composition of claim 1 which includes up to about10 percent by weight of the bitumen composition of another hydrocarbonor blown bitumen.
 13. The composition of claim 7 wherein the inertfiller material comprises from about 40 to 65 percent by weight of thebitumen composition.
 14. The composition of claim 13 wherein the fillermaterial comprises limestone.
 15. The composition of claim 8 wherein thesheet material comprises low melting point non-woven polypropylene sheetmaterial.
 16. The composition of claim 1 wherein the low densitypolyethylene has a density of about 0.90 to 0.930 g/cm³ and the highdensity polyethylene has a density of about 0.935 to 0.970 g/cm³.